1. Field of the Invention
The present invention relates to a vehicle, such as an automobile, having an internal combustion engine, one or more batteries powering electrical devices on the vehicle, and an electrical connection box which is mounted on the vehicle, and also to an electrical connection box for use in such a vehicle.
2. Description of the Related Art
Normally one secondary battery, e.g., rechargeable battery, having a rated voltage of 12V and a maximum nominal voltage of 14V is mounted on an internal combustion engine type automobile. A voltage up to the maximum voltage of 14V is applied from the battery to an internal circuit composed of bus bars and the like accommodated in an electrical connection box. The power supply is distributed by the internal circuit of the electrical connection box. The operation of electric/electronic component parts mounted on the vehicle is controlled through electric wires connected with the internal circuit.
On a goods vehicle, such as a lorry or truck, a rated voltage of 24V and a maximum voltage of 28V are applied to a circuit, by a battery structure.
In recent years, electric/electronic component parts have been mounted, in increasing numbers, on a vehicle, and there is an increase in the electric current which is applied to each electric/electronic component part. For example, the electric power required to drive a fan is conventionally 130 watts, but has become 260 watts in recent years. At the rated voltage of 12V of the battery, it has become impossible to operate suction and exhaust devices of an engine, an electromotive power steering, and the like devices, requiring a high voltage such as 36V. Therefore, they are mechanically operated by the driving force of the engine.
With the increase of the electric current applied to each electric/electronic component part, the diameter of the electric wires used has become larger. Further, with rapid increase of the number of electric/electronic component parts, the number of electric wires has increased recently, which has increased the diameter of a wire harness including a bundle of electric wires. Consequently, the weight of the electric wires to be wired on a vehicle body has increased.
As described above, if the power supply from the battery is incapable of operating the suction and exhaust devices of the engine, they are mechanically operated. In this case, it is impossible to accomplish fine control of the operation of the suction and exhaust devices. Further, much fuel is consumed, which pollutes the environment. Accordingly, it is preferable to operate the suction and exhaust devices of the engine and the like not mechanically but electrically by the power supply from the battery.
In the case where the circuit is so constructed that a voltage higher than 14V can be applied to the circuit of the electrical connection box composed of bus bars and the like, it is possible to reduce the required electric current and thus the diameter of the electric wires and the size of a bundle of a plurality of electric wires (e.g., wire harness). Therefore, it is possible to reduce the weight of the electric wires.
Further, with the application of a high voltage to the circuit composed of bus bars and the like, it is possible to control the operation of the suction and exhaust devices, the power steering motor, and the like not mechanically or hydraulically but electrically. In this case, it is possible to accomplish fine control of the operation of suction and exhaust devices and the like. Further, fuel consumption can be reduced, which reduces pollution.
It is preferable to apply a high voltage of about 42V to the electromotive power steering motor, the suction and exhaust devices of the engine, the fan, and/or other devices requiring a high voltage. On the other hand, in an automobile, it is preferable to apply the rated voltage of 12V (maximum voltage: 14V) to signal-generating devices of the electric/electrical components parts and coils of relays.
However, if the electrical connection box for distributing the power supply is provided with a circuit to which a low voltage up to the maximum voltage of 14V (28V in a truck) is applied and with a circuit to which a high voltage of about 42V is applied, a leak current is liable to be generated between the two circuits, owing to the potential difference. Such a leak current may particularly occur if water or dirt enters the electrical connection box. The leak current is also liable to be generated in the circuit to which the high voltage of about 42V is applied.
It is an object of the present invention to prevent or reduce generation of leak currents in an electrical connection box, thereby permitting a circuit to which electric current having a low voltage is applied and a circuit to which electric current having a high voltage is applied.
According to the present invention, there is provided a vehicle having an internal combustion engine providing motive drive of the vehicle, a first, low-voltage battery structure including at least one secondary battery (rechargeable battery), and having a nominal maximum output voltage selected from a range of form about 14V and to about 28V, a second, high-voltage battery structure including at least one secondary battery (e.g., rechargeable battery), and having a nominal maximum output voltage higher than that of the first battery structure and not more than 200V, a plurality of electrical devices powered by the first and second battery structures, and an electrical connection box containing an electrical circuit therein which effects connection between the first and second battery structures and the plurality of electrical devices.
The electrical circuit includes an insulation material in a generally plate-like shape and, embedded in the insulation material, at least one first bus bar connected to the first battery structure and at least one second bus bar connected to the second battery structure, whereby in operation the first and second bus bars are at different potentials, the insulation material electrically insulating the bus bars from each other.
Each of the first and second bus bars has at least one connection tab projecting out of the insulation material.
In a second aspect, the invention provides an electrical connection box for use in the vehicle of the invention described above. The electrical connection box contains an electrical circuit including an insulation material in a generally plate-like shape and, embedded in the insulation material, at least one first bus bar adapted to be connected in use to the first battery structure and at least one second bus bar adapted to be connected in use to the second battery structure, whereby in operation the first and second bus bars are at different potentials. Each of the first and second bus bars has at least one connection tab projecting out of the insulation material.
In conventional vehicle junction boxes, bus bars are fixed to the surface of an insulation plate. But in the present invention, the bus bars are embedded in the insulation material. More specifically, an insulation material, such as synthetic resin, is filled in the space where a leak current is liable to be generated, namely, the space between the low-voltage bus bar and the high-voltage bus bar and the space between the high-voltage bus bars. Thus, it is possible to prevent or minimize generation of leak currents.
Because the bus bars are embedded in the resin, the low-voltage bus bar and the high-voltage bus bar can be disposed at random in the same body of insulation material. Thus, the construction of the circuit is not limited to a specific one but can be designed freely.
Preferably, a lower portion of the tab of each low-voltage bus bar and high-voltage bus bar is embedded in the insulation material except a portion of the tab to be fitted on a terminal.
Because the tabs formed by bending the bus bars are required to be connected to terminals of an external circuit, the tabs project from the surface of the insulation material. As described above, the tabs are preferably embedded in the material except portions of the tabs to be fitted on terminals. Therefore, it is possible to prevent generation of a leak current although the tabs are adjacent to each other.
Preferably a projection such as a spigot or a rib projects from an insulation board or plate, which is a part of the insulation material. The projection is inserted into a hole formed on each low-voltage bus bar and high-voltage bus bar and is deformed to fix the bus bars to the board. The low-voltage bus bar and the high-voltage bus bar are covered by a surface body of resin, e.g. in a die or mold, to cover the bus bars with the resin after the fixing of the bus bars to the board. In this manner, it is easy to manufacture the circuit.
It is preferable that the high voltage to be applied to the high-voltage bus bar is about 42V. In this case, the voltage applied to the high-voltage bus bar at 42V may be provided by connecting in series three batteries each having a rated voltage of 12V (nominal maximum voltage: 14V) generally used in automobiles. Needless to say, it is possible to use a single battery having a maximum voltage of 42V. The reason why the high voltage to be applied to the high-voltage bus bar is preferably set to about 42V is partly because using a voltage close to or above 50V for the high-voltage bus bar may be more dangerous. The present inventors have conducted salt water experiments in order to ascertain the degree of risk when applying a voltage of 42V in an electrical junction box suitable for use in an automobile engine compartment, as follows:
1 ml of salt water was injected into each terminal hole of the casing of a junction box which had bus bars disposed inside. Electrical components, such as relay, fuse, connectors etc., were mounted on the casing. A voltage of 42V was applied to bus bars of the junction box for 8 hours and suspended for 16 hours. This was repeated twice. There was initially no change to the bus bars and electrical components. However, after the third repetition, it was found that extra electric current passed between the bus bars generating heat and a portion of bus bars was melted. The heat also melted resin around bus bars such as an insulation plate, casing and resin portion of electrical components adjacent the casing.
Accordingly, it was confirmed that in consideration of normal use condition of an automobile, the application of the electric power at 42V to the electric/electronic component parts should not cause a problem.